The invention relates to a production method of multi-layer information record carriers, and more particularly, to a production method of manufacturing multi-layer information record carriers by replacing a substrate that comprises a signal duplication layer with a metallic stamping plate.
Along with the advent of the information and multimedia era, there is an increasing need for greater record density and capacity of record carriers by 3C productsxe2x80x94computers, communications, and consumer electronics. The record density of the optical information record carrier that uses a red laser as the light source for reading information is relatively restricted because of an optical diffraction limit. So far, certain principles and methods of increasing the record density of optical information record carriers have been introduced. The more important ones for which the technology for the manufacturing processes have recently been developed include: a reduction of the wavelength of the laser light source for reading, such as by replacing the red laser with a blue laser as the light source for reading, or increasing the caliber of a lens. Additionally, improvements may be made in the method of encoding digital signals or using the so-called super-resolution near-field optical structured DVD recording. The record density can be effectively increased by means of the above methods.
Another technology for increasing the record capacity of an information record carrier (such as DVD) involves providing multiple layers for the information record carrier. In other words, the technology creates a 3-D multi-layer record carrier, multiplying its record capacity. The current methods for manufacturing multi-layer information record carriers include the method disclosed in U.S. Pat. No. 5,059,473xe2x80x94injection molding, by which a central substrate is created by injection and signals are formed on both sides of the substrate. A signal duplication layer is then put on both sides of the substrate by means of plating, and eventually a protective plate is affixed to the substrate with transparent glue. Another method is called surface transfer. Given the low adhesive affinity between Polycyclohexylethylene (PECH) and Aluminum, the method of surface transfer involves plating a metallic layer (for example, Aluminum layer) that acts as a total reflection layer on a substrate made from Polycyclohexylethylene by means of high-pressure injection molding.Affixing, with optical glue, the Polycyclohexylethylene substrate to another substrate that is full of signals and is plated with a semi-reflection layer, then the optical glue is subjected to curing through the ultra violet light, and finally when the two substrates are separated from each other. Due to the low adhesive affinity between Polycyclohexylethylene (PECH) and Aluminum, the Aluminum layer is separated from the PECH substrate and then it is affixed to another substrate, becoming a single-side dual-layer DVD. A dual-side dual-layer digital video disc, DVD, is formed when two single-side dual-layer substrates with a thickness of 0.6 mm are affixed to each other through their total reflection layers. Both of the two aforesaid methods may produce a multi-layer information record carrier at a single-side dual-layer level or any higher level. However, both methods employ a high-pressure manufacturing process, thus their defective rates remain high.
In addition, there are some other methods for manufacturing single-side dual-layer record carriers. Firstly, in U.S. Pat. No. 5,171,392, a reflective layer is plated on a substrate for which a signal layer has been cast in advance. It is then affixed to a stamping plate by means of resin. The stamping plate is then detached from the substrate and the second record layer is formed. Finally, the second reflective layer is plated on the substrate and a protective layer is added onto the substrate. Similarly, in U.S. Pat. No. 5,708,652, a reflective layer is also plated on a substrate for which a signal layer has been cast in advance, but a high molecular layer is placed in between the substrate and the stamping plate. The high molecular elements are then melted down at a high temperature and a high pressure and they flow into the grooves of the stamping plate. The melted elements are solidified by ultra violet light. Finally, the stamping plate is detached. The aforesaid methods employ a relatively expensive metallic stamping plate. Take U.S. Pat. No. 5,874,132 as an example. Its manufacturing process primarily involves plating a reflective layer and the first record layer on a substrate beforehand, and pouring high molecular resin while turning a roller-shaped stamping plate. The second record layer is formed provided that their relative speeds are well controlled. As regards this method, attention should be paid to the position of the substrate relative to the stamping plate as well as applying forces to the substrate evenly. Another shortcoming of the method is that it is difficult to produce roller-shaped stamping plates.
In short, all of the above methods require a metallic stamping plate with the exception of surface transfer. However, a PECH stamping plate may not be recycled, making it impossible to cut manufacturing costs. As for the production of multi-layer information record carriers, both surface transfer and injection molding can produce multi-layer information record carriers at a single-side dual-layer lever or higher, though both of them involve a high-pressure manufacturing process, thus their defective rates remain high. U.S. Pat. Nos. 5,171,392, 5,708,652 and 5,874,132 can only produce single-side dual-layer record carriers.
In view of this, the object of the invention is to use a method, which is suitable for mass production, to manufacture multi-layer information record carriers. The production method for multi-layer information record carriers mentioned in the invention involves forming a signal duplication layer on a substrate that contains signals. The substrate that comprises the signal duplication layer replaces a metallic stamping plate for generating a signal layer, thus the manufacturing cost of multi-layer information record carriers is reduced. In addition, the simple, speedy manufacturing process facilitates the creation of automation facilities for mass production and the enhanced production of good products.
The first method of the invention involves forming a signal duplication layer on a substrate that contains signals, so that it becomes the stamping plate for the signal duplication layer. Then the signal duplication layer is coated with a solution of high molecular resin. Illumination with ultra violet light causes the resin to cure and the signal duplication layer is turned into a signal layer. The signal layer is coated with another layer of high molecular resin solution and is thus turned into a holding layer in order to hold a second substrate that contains signals and comprises a semi-reflection layer. Again, illumination with ultra violet light causes the curing of the holding layer so as to glue the second substrate and the signal layer together. Since the adhesive force between the signal layer and the signal duplication layer of a high molecular material is smaller than that between the signal layer and the holding layer of the second substrate, the signal layer and the signal duplication layer are separated from each other. A total reflection layer is plated on the signal layer so as to form a single-side dual-layer information record carrier. Or, a semi-reflection layer is plated on the signal layer, the single-side dual layer information record carrier is treated as a substrate, and the aforesaid procedure is repeated. Both the signal duplication layer that acts as a stamping plate and the substrate can be recycled repeatedly. The method produces multi-layer information record carriers at a single-side triple-layer level or higher.
The second method of the invention involves forming a signal duplication layer on a substrate that contains signals. A solution of high molecular resin is then smeared and spread over the signal duplication layer, and the signal duplication layer is turned into a signal layer. Directly affix it to the second substrate that contains signals and comprises a semi-reflection layer. Illumination with ultra violet light causes curing of the signal layer. Glue the second substrate and the signal layer together, and detach the signal duplication layer from the signal layer. The signal layer is plated with a total reflection layer so as to create a single-side dual-layer information record carrier. Or, a semi-reflection layer is plated on the signal layer, the single-side dual layer information record carrier is treated as a substrate, the aforesaid procedure is repeated, and multi-layer information record carriers are produced at a single-side triple-layer level or higher. In the second method, a single layer of high molecular solution is used as a signal layer and a holding layer simultaneously. To enable the smooth detachment of the signal duplication layer from the signal layer, different materials are employed to form the signal duplication layer and the semi-reflection layer. Different materials adhere to the signal layer under different degrees of adhesive force. The adhesive force between the signal layer and the signal duplication layer must be smaller than that between the signal duplication layer and semi-reflection layer, in order to allow the signal layer and the signal duplication layer to be separated from each other.